Based on the importance of the avian model for delineating cell- mediated and humoral immune response, the broad objections are to obtain basic information on the following: (1) Identity of immune response (Ir) genes in chickens and the role of T- and B-cells in genetic- determined immune responsiveness. The relation of the Ir genes to the major histocompatibility complex is being studied. At present the anti- GAT response is known to be related to the blood group antigen B; whether different genes are involved in related polypeptide antigens is being investigated. (2) The location of chicken allotypes. At present we have found more than one allele present on the 7S immunoglobulin; their locations are being sought by analysis of the H and L chains. (3) A search is being made for cross-reacting idiotypes and their relationship to clonal synthesis.